[autoroll] Add tooltips to mode change buttons
[autoroll] Add tooltips to mode change buttons

Change-Id: I2a069db3407011615d82ba1f21a97fbf13bed2cb
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/542120
Reviewed-by: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>
Commit-Queue: Eric Boren <0e499112533c8544f0505ea0d08394fb5ad7d8fa@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot